The present invention concerns vacuum-type boosters intended, especially, to assist the braking of motor vehicles.
These boosters function perfectly well and have been known to persons skilled in the art for a long time. Such a booster is, for example, described in U.S. Pat. No. A-4,756,232. No complete description of such a booster or of its method of operation will therefore be recapitulated here.
Such a booster comprises a case divided internally into a vacuum chamber and a working chamber by a piston comprising a valve means possessing a double valve enabling in the rest position, a communication between the two chambers which are then isolated from the environment and, in the working position, an isolation of the vacuum chamber and a communication between the working chamber and the environment at atmospheric pressure. The valve means is normally controlled by means of an actuating rod extending out of the case.
Due to the sophistication of certain systems, it may be desirable to control the valve means independently of the actuating rod. In the application to brake boosting for vehicles, especially, it may be desirable to provide automatic braking independently of the driver's will, for example to provide braking of a wheel tending to spin, or in response to the detection of an obstacle by any means of the onboard radar type.
From U.S. Pat. No. A-4,608,825, it is known a brake arrangement for automatically applying the brakes when the driver leaves the seat of the vehicle. The operating shaft has a passageway therein defining a valve seat for providing a communication with air controlled by a solenoid valve member. However this brake system requires many modifications to the booster system.